These tutorials are from 2014. While they provide a good overview of R syntax, a lot has been added to the R-verse such as dplyr, which the author primarily used for his Trump Tweets blog post yesterday.

If you are interested in learning R, you may want to read the R for Data Science book (http://r4ds.had.co.nz/) book by dplyr (and ggplot2) author Hadley Wickham.

Relatedly, I have my own (slightly more complicated) notebooks using R/dplyr/ggplot2, open-sourced on GitHub, if you want further examples of real-world analysis with publically-available data along the lines of the Trump Tweet analysis:

Processing Stack Overflow Developer data: https://github.com/minimaxir/stack-overflow-survey/blob/mast...

Identifying related Reddit Subreddits: https://github.com/minimaxir/subreddit-related/blob/master/f...

Determining correlation between genders of lead actors of movies on box office revenue: https://github.com/minimaxir/movie-gender/blob/master/movie_...